Float shoe apparatus



p 8, 1970 w. R. LEWIS 3,527,299

FLOAT SHOE APPARATUS Filed NOV. 25, 1968 flEE:Z

United States Patent 3,527,299 FLOAT SHOE APPARATUS William R. Lewis,Wichita Falls, Tex., assignor, by mesne assignments, to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware Filed Nov. 25, 1968,Ser. No. 778,409 Int. Cl. E21b 23/00 US. Cl. l66-l84 Claims ABSTRACT OFTHE DISCLOSURE A float shoe apparatus for cementing well casings whichincludes an outer tubular member connectable to the lower end of astring of well casing, a nose plug secured to the lower end of thetubular member, an outer sleeve movably mounted on, and concentricallysurrounding a medial portion of, the tubular member, an inner tubularmember secured in, and opening concentrically through, the nose plug,and a valve internal piston assembly mounted concentrically within theouter tubular member and slidable axially therein. The outer tubularmember is axially slotted at a medial portion which underlies aninflatable rubber packing sleeve forming a portion of the outer sleeve,and downward movement of the internal piston in the outer tubular memberforces fluid into the packing sleeve to expand it into contact with thewalls of a well bore. Piston type pressure relief valves are disposed inthe nose plug and vent fluid from the interior of the apparatus when thepressure acting to expand the packing sleeve exceeds a predeterminedvalue.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to well tools, and more particularly, to apparatus connectableto the lower end of a casing string and useful in closing the end of thecasing string to impart buoyancy thereto, and for permitting acementitious material to be pumped between the casing and well bore.

Brief description of the prior art In the procedure of completing oilwells, it is the practice to drill a well bore, then run a casing intothe well bore. The hole is then often conditioned by pumping circulatingfluid out through the lower end or shoe of the casing. Finally, thecasing is cemented in place by positioning cement above the lower end ofthe casing in the annulus between the casing and the surrounding earth.

To accomplish the casing positioning and cementing operations, a fittingtermed a float shoe is usually secured to the lower end of the casingstring and functions to close the lower end of the casing during itsdescent in the well bore, and to selectively direct cementitiousmaterial to a location above the lower end of the casing and around theoutside thereof when the casing is in position. Float shoes of the typepreviously employed usually include a check valve which closes toprevent drilling fluid from entering the interior of the casing and thusto maintain the casing in a relatively buoyant state as it is floatedinto position in the bore. The check valve will open, however, to permitfluids to be pumped through the casing from the surface in order tocondition the well if desired. Many float shoes previously in use also3,527,299 Patented Sept. 8, 1970 include mechanism by which aninflatable packing sleeve forming a part of the float shoe can beexpanded with a suitable fluid to form a plug blocking or sealing olfthe annulus between the casing and well bore, and that portion of thebore which is below the lower end of the casing. A float shoe of thistype is described in Austin U.S. Pat. 2,845,130.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present inventioncomprises a tubular member connectable to the lower end of a string ofwell casing and having an upper end and a lower end; plug means securedto the lower end of the tubular member; and outer sleeve means movablymounted on, and concentrically surrounding a media portion of, thetubular member. A valved internal piston assembly is mounted within thetubular member and is movable axially therein. The tubular member isaxially slotted, and the outer sleeve means includes an inflatableresilient packing sleeve which overlies a portion of the slots in thetubular member, and a rigid sleeve portion which is connected throughthe slots to the valved internal piston assembly.

The plug means is provided with at least one pressure relief valve whichplaces the well bore in communication with an annulus between a portionof the internal piston and the tubular member. As the internal pistonmoves axially downwardly to reduce the volume of this annulus, the fluidoccupying the annulus is forced through the slots in the tubular memberagainst the inflatable packing sleeve to expand it into contact with theWalls of the Well bore. If an excessive pressure is developed on thepacking sleeve tending to rupture it, the pressure relief valve in theplug means opens to relieve this pressure by venting the trapped fluidto the well bore. In this manner, the well can be quickly, safely andeffectively packed 01? for cementing the casing in position whileleaving the bottom of the hole uncased.

An important object of the invention is to provide a float shoeapparatus which can be utilized to float a well casing to a positionnear the lower end of the well bore, and then cement the casing inposition without circulating cement into the bottom of the well.

Another and more specific object of the invention is to provide a floatshoe for use in positioning oil well casing, which float shoe isadaptable to wider variations in well bore diameters without rupture orseverance of an inflatable resilient packing sleeve forming a portion ofthe float shoe.

A further object of the invention is to provide a float shoe of theinflatable packing sleeve type in which the packing sleeve can beinflated by means of fluids located in the well bore when the float shoeand associated casing are lowered in the bore.

Yet another object of the invention is to provide a float shoe in whicha preselected pressure applied to a. fluid directed down a casing stringto which the shoe is attached can be depended upon to actuate the shoeand thereby to expand an inflatable packing sleeve forming part of theshoe.

An additional object of the invention is to provide an improved floatshoe which is characterized in having a long and relatively trouble-freeoperating life.

Additional objects and advantages of the invention will become apparentas the following detailed description of the invention is read inconjunction with the accompanying drawings which illustrate theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of thefloat shoe of the invention as it appears when being lowered in the Wellbore and prior to inflating the resilient packing sleeve. An alternateposition of a check Valve employed in the float shoe is shown in dashedlines, as is an auto-fill bridge tube which may optionally be employedin combination with the float shoe.

FIG. 2 is a sectional view similar to FIG. 1, but showing the float shoein its stationary, packed otf status.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Thefloat shoe apparatus of the invention is depicted in the figures of thedrawings as disposed in a well bore designated generally by referencenumeral 10. The float shoe includes an elongated tubular member 12having an internally threaded box portion 14 at the upper end thereofwhich threadedly engages the lower end of a casing string 15. Secured inthe upper end of the elongated tubular member 12 is a back pressurevalve assembly 16 having a bore 17 therethrough which is closed by apivotally mounted valve member 18. The valve member 18 is spring biasedto the closed position illustrated in solid lines in FIG. 1. The openposition of the valve member 18 is shown in dashed lines.

Threaded into the lower end of the elongated tubular member 12 is arounded nose plug 20 which has a bore 22 extended concentricallytherethrough, and carrying threads 24 for threaded engagement with aninternal elongated tubular member 26. The upper end of the internaltubular member 26 is beveled outwardl as indicated by reference numeral27. The internal tubular member 26 has a plurality of contiguous annularserrations 28 formed in its internal wall intermediate its length. Eachserration 28 has an upper surface 28a disposed in a plane passed at aright angle to the axis of the internal tubular member 26, and also hasa lateral surface 28b which is inclined at an angle with respect to thisaxis, and thus each serration is generally V-shaped in crosssectionalconfiguration. The purpose of this configuration of the serrations 28will be hereinafter described.

Extending axially in the nose plug 20, and spaced radially outwardlyfrom the inner tubular member 26 and circumferentially from each other,are a plurality of spring retainer bores 32. Radially extending pins 34are secured across the upper ends of the spring retainer bores 32 tofunction as positive stops for pressure relief valve pistons 36 locatedin each of the bores. Each of the pressure relief valve pistons carriesa suitable sealing ring 38, and is biased upwardly in the bore by anelongated helical spring 40. Communicating with the lower portion ofeach of the spring retainer bores 32 is a radial pressure relief orifice42 which extends through the side of the nose plug 20 into communicationwith the surrounding well bore 10.

Secured by welding or other suitable means to the lower portion of theelongated tubular member 12 is a packing sleeve anchor ring 46. Aninflatable, resilient, cylindrical packing sleeve 48, which may besuitably constructed of rubber, has its lower edge bonded to the packingsleeve anchor ring 46 and extends upwardly around the tubular member 12in concentric relation thereto. It will be noted that in the status ofthe float shoe illustrated in FIG. 1, the inflatable resilient packingsleeve 48 extends partially over and partially covers a plurality ofelongated, axially extending, circumferentially spaced slots 50 formedin the wall of the tubular member 12 intermediate the length thereof. Atits upper end, the inflatable resilient packing sleeve 48 is bonded to arigid outer sleeve 52 which slidingly surrounds an intermediate portionof the tubular member 12 and extends over a portion of the slots 50therein. The outer sleeve 52 is provided near its upper end with one ormore annular grooves which carry sealing rings 56 sealingly engaging theouter surface of the tubular member 12. It will further be noted thatthe elongated tubular member 12 also carries at least one externallylocated annular groove and sealing ring 60 at a location below the slots50, and the sealing rings 60 serve to sealingly engage the rigid outersleeve 52 during a cementing operation in Which the inflatable resilientpacking sleeve 48 is expanded to a packed oft position as depicted inFIG. 2 of the drawings. The use of the apparatus in this respect will behereinafter explained in greater detail.

Disposed within the elongated tubular member 12 and between the noseplug 20 and the back pressure valve assembly 16 is a valved internalpiston assembly designated generally by reference numeral 62. The valvedinternal piston assembly 62 includes an inner sleeve 64 positionedconcentrically and slidingly within the tubular member 12, and anelongated tubular plunger 66 which is threadedly engaged at its upperend with the inner sleeve 64. The tubular plunger 66 in the illustratedembodiment of the invention is upwardly and outwardly flared at itsupper end to provide a flange 68 which aids in guiding into the tubularplunger, a spherical valve member dropped down the casing as hereinafterdescribed. The tubular plunger 66 further carries adjacent its upperend, an internal thread 67 which can be used to threadedly engage anoptionally employed bridge pipe 70 illustrated in dashed lines. Thebridge pipe 70, when utilized in combination with the float shoeapparatus of the invention, bridges across the space between the valvedinternal piston assembly 62 and the back pressure valve assembly 16 andprojects into the bore 17 through the back pressure valve assembly so asto retain the valve member 18 in its open position. This permits thefloat shoe and the casing string attached thereabove to become filledwith mud and well fluid as the float shoe is lowered in the well bore10. This is an optional or alternative utilization of the float shoeapparatus of the invention which is sometimes desirable when certainother equipment or apparatus is located in the casing uphole from thefloat shoe. Nothing more will be said in the present applicationconcerning this possible mode of utilizing the float shoe since, in mostcases, the method of operation and use of the float shoe will entailclosing the valve member 18 when the well casing is being lowered to thebottom of the well bore 10 for purposes of cementing it in position.

At the lower end of the tubular plunger 66, the plunger threadedlyengages an internal valve seat 72. Surrounding the lower end portion ofthe tubular plunger 66 are two seal ring sets 74 and 76, and a lockingring 78 which is disposed between the two sets of seal rings. Thelocking ring 78 is of triangular cross-sectional configuration and isretained loosely in a V-shaped groove formed in the side of the tubularplunger 66, so that a portion of the locking ring projects radiallyoutwardly from the outer surface of the plunger for a purpose more fullyhereinafter described. It should be mentioned that the locking ring 78is characterized by a resiliency which permits constriction of the ringto a smaller diameter in which it is substantially entirely confinedwithin its associated V-shaped groove.

The outer sleeve 52 and inner sleeve 64 are interconnected forsimultaneous movement with respect to the elongated tubular member 12 bya plurality of threaded bolts 80 which are extended through the slots 50formed in the elongated tubular member 12. A shearing ring 82, which ispreferably constructed of rubber, in located in an annular space whichis defined by a pair of opposed communicating grooves 84 and 86 formedin the inner sleeve 64, and in the internal wall of the elongatedtubular member 12, respectively. The nature of the shearing ring 82 issuch that it will be sheared diametrically when the valved internalpiston assembly 62 is forced downwardly in the elongated tubular member12 for the purpose of expanding the inflatable packing sleeve 48 ashereinafter described. Adjacent its upper end the inner sleeve 64carries a plurality of seal rings 88 which sealingly engage the tubularmember 12.

OPERATION In the utilization of the float shoe apparatus of theinvention, the float shoe is secured to the lower end of a string ofcasing 15 by threading the upper end portion 14 of the elongated tubularmember 12 on the lower end of the casing string. As the casing string 15having the float shoe apparatus attached to the lower end thereof is lowered in the well bore 10, the valve member 18 of the back pressure valveassembly 16 is retained in a closed position by the spring biasedcharacter of the valve structure, and in addition, by the pressureacting upwardly thereon by well fluids in the well bore 10 which enterthe float shoe through the nose plug 20. Thus, these fluids areprevented from passing through the bore 17 in the back pressure valveassembly 16 to enter the casing string, and the string is thereforecharacterized in having suflicient buoyancy to permit it to float slowlydownwardly in the well bore. It should be noted, however, that the checkvalve characteristic of the back pressure valve assembly 16 will permitwell conditioning fluids to be pumped down the casing string 15, throughthe float shoe, and into the well bore 10 of this is desired.

In many types of well casing operations, it is desirable to extend thecasing string to a point fairly low in the Well bore 10, but spacedvertically from the bottom of the well bore. In other words, the bottomportion of the well bore is permitted to remain uncased, and theoperation which is carried out entails cementing the casing string inposition in the well bore by locating cement between the casing and thewall of the well bore, but above the uncased bottom portion of the wellbore. To this end, once the casing string 15 and the float shoeapparatus at the lower end thereof have been lowered in the well bore 10to the desired location, the float shoe is utilized for packing oif thewell bore to prevent cement from by-passing the float shoe and enteringthe uncased lower end portion of the well bore.

In order to pack oh? the well bore 10 in this manner for cementingpurposes, a spherical valve member or ball 92 is dropped down the hollowcasing string 15 and is forced through the back pressure valve assembly16. The spherical valve member 92 then is guided by the flared flange 68into the tubular plunger 66 of the valved internal piston assembly 62and ultimately comes to rest upon the valve seat 72. The possibility offluid being directed downwardly through the casing string and outthrough the tubular member 26 in the lower end of the float shoeassembly is thus eliminated at this time due to the closure of theopening through the valve seat 72 by the spherical valve member 92. Atthe time that the valve member 92 is dropped through the casing stringto rest upon the valve seat 72, the annular space 94 between the tubularplunger 66 and the elongated tubular member 12, as well as between thelatter member and the inner tubular member 26, has been filled withfluid from the well. During low ering of the casing string 15 and floatshoe, this well fluid has been free to pass into this annulus throughthe space between the lower end of the tubular plunger 66 and the upperend of the inner tubular member 26. In other words, the spacesurrounding the tubular plunger 66 and the internal tubular member 26will have been filled with mud and well fluid which is forced into thisspace during the descent of the casing string and attached float shoe.

When the spherical valve member 92 has been positioned on the seat 72while the apparatus is in all other respects still in the statusdepicted in FIG. 1, the next step in expanding the inflatable packingsleeve 48 entails the pumping down the casing string 15 of cement whichis to be utilized to cement the casing in position within the well bore10. The cement passes through the back pressure valve assembly 16 byforcing open the valve member 18,

and then necessarily passes downwardly in the bore in the tubularplunger 66. Pressure is thus everted on the entire valved internalpiston assembly 62 in a downward direction, since the cement cannotby-pass the valve seat 72 due to the location thereon of the sphericalvalve member 92. The pressure of the cement acting downwardly on thevalved internal piston assembly 62 forces this assembly downwardlywithin the elongated tubular member 12. As the internal piston assembly62 moves downwardly, the tubular plunger 66 enters the inner tubularmember 26 and sealingly engages the internal wall of this tubular memberthrough the sets of seal rings 74 and 76 carried on the outer peripheryof the plunger. The locking ring 78 is able to resiliently yieldinwardly slightly during the downward movement of the plunger 66 in theinner tubular member 26 so as to permit the plunger to continue itsdownward movement until the locking ring is opposite the V-shapedserrations 28 formed in the internal surface of the inner tubularmember. At this point, the resiliency of the locking ring 78 snaps itoutwardly so that an interlocking engagement between the locking ring 78and one of the serrations 28 occurs to lock the plunger against verticalaxial movement within the inner tubular member 26. The shapes of thelocking ring '78 and each serration 28 are such, however, that downwardmovement of the plunger 66 within the inner tubular member 26 can becontinued if desired.

During the downward movement of the internal piston assembly 62, theouter sleeve 5-2 is carried with the piston assembly due to itssecurement to the inner sleeve 64 by the threaded bolts 80. The downwardmovement of the outer sleeve 52 exerts a compressive force on theinflatable packing sleeve 48 so that this packing sleeve is buckledoutwardly toward the walls of the well bore 10. Simultaneously with thisforced outward movement of the inflatable resilient packing sleeve 48,the downward movement of the inner sleeve 64 reduces the total volume ofthe space existing between the tubular plunger 66 and the inner tubularmember 26 on the one hand, and the inflatable packing sleeve and theouter sleeve 52 on the other. Thus, the fluid which occupied the totaloriginal volume of the annulus between the valved internal pistonassembly 62 and the tubular member 12 is forced outwardly through theslots 50 against the inflatable packing sleeve 48 so that the bulgeinside this packing sleeve is filled with fluid which supports thepacking sleeve in its inflated condition. Continued downward movement ofthe valved internal piston assembly 62 along with the outer sleeve 52eventually brings the lower end of the outer sleeve 52 past the lowerend of the axially extending slots 50 in the tubular member 12.

At this time, fluid from the annulus between the internal pistonassembly 62 and the tubular member 12 can no longer enter the spacebetween the inflatable packing sleeve 48 and the tubular member 12. Bythis time, in many instances, the inflatable packing sleeve will havebeen inflated outwardly until it engages the internal walls of the wellbore 10 in the manner depicted in FIG. 2. When the packing sleeve 48attains this status, the well bore is packed off so that cement whichmay be positioned in the annulus between the tubular member 12 and thewalls of the well bore cannot by-pass the inflatable packing sleeve 48to enter the lower end portion of the well bore.

Two of the important features of the present invention are theadaptability of the float shoe apparatus to employment in well bores ofdiffering diameters, and the lengthened opearting life withoutmalfunction which characterizes the float shoe apparatus. Both of theseadvantages are in large part attributable to the pressure relief valveconstruction which characterizes the apparatus. Thus, for a relativelysmall diameter well bore 10, the inflatable packing sleeve 48 cannot beexpanded a very great distance with respect to the tubular member 12before it is prevented from further expanding due to contact with thesurrounding wall of the well bore. At this time, additional fluid can beforced into the inflatable packing sleeve 48 by the descending internalpiston assembly 62 only at the risk of rupturing the packing sleeve orsevering its bonded connection with the anchor ring 46 or the outersleeve 52 so as to lose fluid from the inside of the sleeve and fail toproperly pack off the well bore. This danger is alleviated with thepresent invention, however, by the inclusion in the nose plug 20 of thepressure relief valves constituted by the pistons 36 and the associatedhelical springs 40. The springs 40 are preselected so that, at thepredetermined pressure, the springs will yield sufliciently to permitthe pistons 36 to move down in the spring retainer bores 32 to a pointwhere fluid can escape through the pressure relief orifices 42. Thus,when the pressure acting outwardly on the inflatable packing sleeve 48becomes excessive, and the yield point or rupture point of the packingsleeve is approached, the pressure relief valves constituted by thepistons 36 and springs 40 will be actuated to vent fluid from theannulus between the inner tubular member 26 and the tubular member 12 tothe well bore through the side of the nose plug 20.

Once the internal piston assembly 62 is moved downwardly within thetubular member 12 to the point where the threaded bolts 80 havecontacted the bottom of the slots 50 to limit further movement of theinternal piston assembly and outer sleeve 52, the locking ring 78 willsnap into interlocking engagement with one of the serrations 28 formedin ther inner wall of the internal tubular member 26. It will further benoted that at this time, the upper end of the outer sleeve 52 has moveddownwardly, along with the inner sleeve -64, to a point where the upperend of each of the slots 50 is uncovered, and the slots therefore placethe inside of the tubular member 12 in communication with the well bore.It is therefore possible at this time to pump cement down the casingstring 14, through the back pressure valve assembly 1'6 and into thetubular member 12. The cement cannot pass down through the lower end ofthe float shoe apparatus and out of the nose plug 20, since this flowchannel is obstructed or blocked by the spherical valve member 92. Thecement will therefore pass outwardly through the upper end of the slots50 into the annulus surrounding the float shoe apparatus, and will fillthis annulus above the inflatable packing sleeve 48. By continuedpumping of the cement in this fashion, the casing can be cemented inposition without introducing any of the cement to the lower end portionof the well bore.

Upon completion of the cementing of the casing in the manner described,a drill is then extended through the casing into the float shoeapparatus, and the cement which may have set up therein, along with thespherical valve member 82 and the valve seat 72, are drilled out by thedrill to permit fluids to be produced from the well.

Although a specific embodiment of the present invention has been hereindescribed in order to provide an example of the manner in which theinvention is to be practiced, it will be understood that various changesand innovations can be made in the depicted and described structurewithout departure from the basic principles of the invention. Allchanges and modifications of this type there therefore deemed to bewithin the spirit and scope of the present invention except as the samemay be necessarily excluded by the appended claims or reasonableequivalents thereof.

What is claimed is:

1. Float shoe apparatus comprising:

a first tubular member having an upper end adapted for connection to awell casing and having a lower end, said first tubular member furtherhaving at least one axially extending slot formed therethroughintermediate its length;

outer sleeve means surrounding said first tubular member and the slotstherein and including 8 a rigid outer sleeve slidably surrounding saidfirst tubular member, and an inflatable packing sleeve around said firsttubular member and having an upper end secured to said outer sleeve anda lower end connected to said first tubular member below said slots;plug means secured to the lower end of said first tubular member andincluding at least one pressure relief valve placing the interior of thefirst tubular member in communication with the exterior thereof whensaid relief valve is open; and

a valved internal piston assembly above said plug means in said firsttubular member and movable axially therein toward said plug means toforce a fluid from the interior of said first tubular member throughsaid slots into said inflatable packing sleeve, said valved internalpiston assembly being secured through said slots to said rigid outersleeve for movement therewith.

2. Float shoe apparatus as defined in claim 1 wherein said internalpiston assembly comprises:

an inner sleeve slidingly and sealingly engaging the interior of saidfirst tubular member and secured through said slots to said rigid outersleeve;

a tubular plunger secured to said inner sleeve and movable therewith toa position sealingly engaging said plug means to prevent fluid flowthrough said plug means to a space between said tubular plunger and saidfirst tubular member.

3. Float shoe apparatus as defined in either claims 1 or 2 wherein saidplug means comprises:

a nose plug secured in the lower end of said first tubular member andhaving said pressure relief valves therein; and

an inner tubular member secured in, and opening through, said nose plug,said inner tubular member being spaced downwardly from said valvedinternal piston assembly in one position of the piston assembly, andsealingly engaging a portion of the piston assembly in a second positionof the piston assembly to form therewith an isolated, continuous fluidpassageway through the nose plug and valve piston assembly whichcommunicates the interior of the first tubular member above the pistonassembly with the outside of the nose plug.

4. Float shoe apparatus as defined in either of claims 1 or 2 andfurther characterized as including a back pressure valve assemblypositioned in said first tubular member above said valved internalpiston assembly for preventing fluid flow upwardly in said first tubularmemher.

5. Float shoe apparatus as defined in claim 2 wherein said inner sleeveand outer sleeve each have a lower portion extending over andobstructing an upper portion of said axially extending slots when saidinternal piston assembly is in a first position in said first tubularmember, and each have an upper portion extending over and obstructingonly the lower portion of said axially extending slots when saidinternal piston assembly is moved downwardly to a second position.

6. Float shoe apparatus as defined in claim 5 and further characterizedas including rigid connecting means extending through at least one ofsaid slots and interconnecting said inner sleeve and said outer sleeve,said rigid connecting means limiting movement of said internal pistonassembly and outer sleeve to movement between said first and secondpositions.

7. Float shoe apparatus as defined in any one of claims 2, 5 or 6 andfurther characterized as including valve means for preventing downwardflow of fluid through said tubular plunger.

8. Float shoe apparatus as defined in any one of claims 1, 2, 5 or 6 andfurther characterized as including a resilient shear ring positionedbetween, and engaging, said internal piston assembly and said rigidouter sleeve for releasably retaining said internal piston assemblyspaced upwardly from said plug means in one operative position of saidfloat shoe apparatus.

9. Float shoe apparatus as defined in any one of claims 2, 5 or 6 andfurther characterized to include a locking ring around said tubularplunger and adapted for snap-in engagement with said plug means whensaid plunger and inner sleeve are moved to said sealingly engagingposition.

10. Floating shoe apparatus as defined in claim 3 wherein each of saidpressure relief valves comprises:

a spring retaining bore in said nose plug and extend ing parallel to thebore through said inner tubular member, and having an upper end and alower end;

a spring in said bore;

bore.

References Cited UNITED STATES PATENTS Lehnhard 166-484 X Bradley166-184 X Litchfield 166-225 Alexander 166225 Nelson 166-225 15 NILE C.BYERS, 111., Primary Examiner

